1. Field of the Invention:
The present invention relates generally to an injection molding apparatus in which a metal material is heated to be half melt, pulverized and poured into a mold to thereby form a metal casting. More particularly, the invention relates to a heating machine in the injection molding apparatus, for heating an ingot of a metal such as a magnesium (Mg) or aluminum (Al) alloy (hereinafter simply called "ingot"), which includes heating means pivotally movable vertically and horizontally so that an ingot can be fed from sideways with respect to the heating means and heated with the heating means positioned in a vertical position, thus enabling reduction in height and size of the injection molding apparatus and prevention of a shock to be exerted to the heating means and ingot upon feeding of the latter.
2. Description of the Related Art:
The present applicant has previously proposed an injection molding apparatus for metal castings as described in Japanese Patent Laid-Open Publication No. 5-285625. With this proposed molding apparatus, an ingot is continuously changed into a slurry, i.e., a semiliquid material. As a consequence, a high throughput can be obtained. This apparatus is next briefly described having reference to FIG. 15.
In FIG. 15, the aforementioned injection molding apparatus for metal castings is generally indicated by reference numeral 200. The apparatus 200 comprises a screw shaft injector 201 and a material feed chamber 202. The material feed chamber 202 has an ingot introduction chamber 203, a heating chamber 204, a constant-temperature chamber 205 that is a heated material-feeding chamber, and a pulverized material storage chamber 207 which are arranged from top to bottom in this order. The pulverized material storage chamber 207 is equipped with a pulverizing cutter 206. The inside of the material-feeding chamber 202 is maintained as a vacuum or an inert gas ambient. The chambers 203 and 204 are isolated from each other by a shutter 208. The chambers 204 and 205 are isolated from each other by another shutter 209.
In the above-described conventional apparatus, an ingot W is heated in the heating chamber 204. The ingot is then transported into the constant-temperature chamber 205 at appropriate timing. The ingot is pulverized by the pulverizing cutter 206. The material is then injected directly or indirectly into a cavity 213 in a mold 212 via the pulverized material storage chamber 207 with a screw 211. The ingot W is made of a metal such as Mg alloy. When this is heated in the heating chamber 204, the ingot becomes partially molten. The apparatus is characterized in that the material is poured into the cavity when the material is in this partially molten state. Consequently, the conventional apparatus is capable of continuously processing ingots. As a result, the apparatus has the advantage that its productivity is high.
In this injection molding apparatus for metal castings, the material path along which the material is introduced, heated, pulverized, and otherwise processed is located over the injector. The material path continues vertically from the top material introduction portion down to the pulverized material storage chamber disposed under the lowest pulverizing cutter. The ingot is shifted vertically from top to bottom of the vertically extending material path. The material is then pulverized and fed into the injection cylinder.
First, the ingot placed vertically is fed into an induction heating device inside the heating chamber from the top introduction chamber located over the heating chamber. It follows that the material introduction chamber is located over the heating chamber. Hence, the material introduction chamber protrudes greatly vertically over the heating chamber.
Therefore, the conventional molding apparatus has the disadvantage that the height is increased by the height of the material introduction chamber which is placed vertically. Since mechanisms for gripping and introducing the material are mounted over the material introduction chamber, the height is increased further. Hence, the outer dimensions and the height of the molding apparatus are increased. This increases the size of the whole apparatus.
Furthermore, in the conventional apparatus, the ingot is introduced from the top material introduction chamber into the heating means (such as the induction heating device inside the heating chamber) in a vertical relation to the heating means. Therefore, when the ingot is introduced into the heating means vertically, it is difficult to carry out the introduction smoothly and stably without inducing impact. As a result, when the ingot is introduced into the heating means, the heating means and the ingot are impacted. For example, where the induction heating device is employed, it is not desirable to impact the induction heating device, because the heating and holding portions are made of ceramic cylindrical members. Furthermore, it is not desired to impact the ingot, stoppers, and other components when the ingot is introduced.
As described above, in the conventional heating machine, the ingot is held vertically within the heating chamber and heated. Then, the ingot is fed vertically without changing the posture. Therefore, it is necessary to mount the material introduction chamber over the heating chamber. Also, the material introduction mechanism is required to be located over the material introduction chamber. Accordingly, we have taken notice of suppressing the height of the heating machine and setting the direction of introduction of the ingot material in such a way that no impact is induced. Based on these considerations, we have made an invention.
The aforementioned bulkiness of the whole machine, impact due to fall of the ingot, and other drawbacks may be circumvented by designing the heating machine so that it can be swung both vertically and horizontally, introducing a material into the heating machine from a side, and then swinging the heating machine into its vertical position. However, in the prior art RF induction heating device, the heating coil is shaped like a ring, the material to be heated is held in position inside the ring-shaped heating coil with holding elements, and the heating coil is energized. Generally, the heating coil is disposed around the material to be heated or on both sides of the material. Therefore, it is substantially difficult to swing the heating machine. If it is attempted to swing the heating machine, then the mechanism for supporting the heating coil, the swinging mechanism, and other mechanisms are made larger. As a result, the weight of the machine is increased. Moreover, the structure of the machine is complicated.
We have found that the heating machine can be swung by winding an RF induction heating coil around a cylindrical member so as to form a heating machine, introducing a material to be heated into the cylindrical member to form a structure for executing RF heating of the material, and holding the cylindrical member so that it can be swung. Thus, we have made another invention.
When a metal ingot is heated by the prior art techniques, it has been necessary that the temperature variations from location to location in the ingot be reduced to a minimum. For this purpose, it is necessary that the positional relation between the heating coil and the ingot be maintained constant. That is, in order to enhance the efficiency of heating, it is desired to narrow the space between the ingot and the ceramic holder that is a cylindrical member.
However, where the space is reduced to improve the heating efficiency, the ingot may get caught during transportation. The ingot may come into contact with the ceramic holder,thus causing the holder to come off. Some problems may thus arise.
We have found that the aforementioned space is maintained at a small constant value by holding the ceramic holder from above and below by means of supports. In this way, we have made a further invention.